In WO2001/68583 there is disclosed a process for the carbonylation of ethylenically unsaturated compounds having 3 or more carbon atoms by reaction with carbon monoxide and an hydroxyl group containing compound in the presence of a catalyst system including:    (a) a source of palladium;    (b) a bidentate diphosphine of formula I,R1R2>P—R3—R—R4—P<R5R6  (I)wherein P represents a phosphorus atom; R1, R2, R5 and R6 independently represent the same or different optionally substituted organic groups containing a tertiary carbon atom through which the group is linked to the phosphorus atom; R3 and R4 independently represent optionally substituted alkylene groups and R represents an optionally substituted aromatic group;    (c) a source of anions derived from an acid having a pKa of less than 3, as measured at 18° C. in an aqueous solution.
The process is carried out in the presence of an aprotic solvent. The preferred hydroxyl containing compounds according to WO2001/68583 are water and alkanols. Notably, the hydrocarboxylation of unsaturated carboxylic acids is not mentioned in this document.